Re-growth of bulk waveguide layers forming butt-joints with MQW structures has been used extensively, such as in the formation of spot-size converters, for example. However, using such structures as low loss, low-defect optical interconnect waveguides to connect different functions within a PIC is emerging. Work investigating the fabrication of devices with substantially different MQW structures has focused on attempting to create good quality butt-joint morphology directly between the two MQW structures (an example conventional butt-joint between different MQW structures is illustrated in FIG. 1). This is challenging and leads to substantial compromises in design and performance. It is also common practice to find one MQW structure which can perform all the necessary functions for a PIC. For applications which require both optical gain and optical phase change, this is also challenging. The shortcomings of direct butt-joint MQW crystal growth is a high-reliability hazard and high optical losses. These issues lead to reduced manufacturing yields, increased cost, and reliability issues. Use of a single common MQW for all-optical functions within a PIC generally leads to design compromises which result in reduced performance. This leads to high-cost products or products which are suboptimal.